The recent portable electronic devices such as a mobile phone, digital camera, etc., use a multilayer printed wiring board having electronic components such as a capacitor, IC and the like mounted on the surface layer thereof.
More specifically, the electronic components to be mounted on such a wiring board are passive parts such as an IC chip, capacitor, resistor, inductor and the like, a liquid crystal device, a display device for digital indication, control devices such as keypad, switches and the like or external terminals such as a USB, earphone and the like.
Various conductor pads corresponding to electronic components are provided together on a printed circuit board, a solder body is formed on each of the conductor pads, and the electronic components are mounted on the solder bodies on the conductor pads.
A typical one of multilayer circuit boards on which the above electronic components are to be mounted is disclosed in the Japanese unexamined patent publication No. H10-13028. As disclosed in the above Japanese unexamined patent publication No. H10-13028, holes for viaholes are formed by lasering, in an insulating rigid substrate having a conductor circuit formed on one side or either side thereof, viaholes are formed by filling a metal paste or a plating material in the holes to form an interlayer-connected circuit board, and two or more such circuit boards prepared as above are stacked sequentially or collectively to produce a multilayer printed wiring board.
In such a multilayer circuit board, two circuit boards are electrically connected to each other by connecting a viahole or a land of the viahole in one of the adjacent circuit boards to a conductor circuit or land of the other circuit board.
Also, the circuit boards are joined, at other areas thereof not contributing to electrical connection between them, to each other with an adhesive layer, prepreg or the like of a thermosetting resin, to thereby form a multilayer structure.
Normally, a solder resist layer to protect the conductor circuit is formed on the surface layer of the above multilayer circuit board or prevailing printed wiring board, a hole is formed in a part of the solder resist layer, and a corrosion-resistant layer of gold or nickel is formed on the surface, exposed in the hole, of the conductor circuit. A solder body such as a solder bump is formed on the surface, having the corrosion-resistant layer formed thereon, of the conductor circuit, and an electronic component such as a capacitor, IC or the like is mounted on the solder bodies formed on the conductor circuit surface.